Reutilisable blasting assemblies



Feb. 3, 1959 Q RY. HAS'LAM ETAL 2,87

' REUTILISABLE BLASTING ASSEMBLIES Filed Aug. 31. 1955 r 2 Sheets- Sheet 1 F G. I INVENTORS ROBERT HASLAM i SAMUEL HENRY DAVIDSON Unite States 2,871,786 REUTILISABLE nLAsriNG ASSEMBLIES Application August 31, 1955,'Serial No. 531,649

Claims priority, application Great Britain September 24, 1954 3 Claims. (Cl. .102-25) The present invention is concerned with improvements in or relating to blasting devices of the kind which contain no explosive or combustible charge of any kind and which rely for their action on the sudden release through suitably disposed venting apertures of gas, e. g. air, introduced into a container portion of the devices when a predetermined pressure is attained.

In devices of this kind there is also absent the electrical means normally used for effecting the decomposition of a charge where blasting is carried out with explosives or with a blasting device having a charge within its container portion which is adapted to release gases when a predetermined pressure is attained and wherein said charge develops a gas pressure on initiation.

A blasting device which brings about a blast as a result of the sudden release of gas introduced into it when a predetermined pressure has been built up therein has the attractive feature that it includes no component or charge that can possibly bring about the ignition of a fiery atmosphere, but its action resembles that of an explosive in that the disruption of the coal by the release of the gases into the borehole is accompanied by the formation of a substantial amount of dust which is objectionable.

A way of reducing dust formation during a blasting operation with explosives by the introduction of a stream of water under pressure into a coal face until the water seeps out from a considerable area around the point of introduction was suggested many years ago and within recent years increasing use has been made of this practice of ,so-called water infusion. In the course of the infusion operation it was noticed that if sufficient water pressure is used there was a tendency for the coal to part and soften during the infusion. This allowed the blasting action of the explosive subsequently introduced into the borehole after the withdrawal of the infusion apparatus to have a greater winning action, although the explosive by itself was not sufficient to bring about the necessary winning action.

It has also been proposed to effect the blasting operation with explosives during the actual infusion operation, that is to say while the borehole is filled with water under pressure. This has the advantage that the water assists in quenching the flame from the explosive and so prevents 1 ignition of a gassy atmosphere, but the hazards in a gassy ice piston which is moved when a water stream is led into the device in a longitudinal direction so that it is distorted radially to seal the borehole. This problem of sealing becomes more dlfiIlCUll'. however if it is required to provide means for introducing gas into the borehole as well as water as wouldbe necessary for any system in which a compressed gas blasting device is used in conjunction with a Water infusion device.

The object of the invention is to provide a blasting apparatus which will permit blasting to be carried out by the sudden discharge of compressed gas, e. g. air, in a water infusion borehole as for instance in an under cut seam of coal or other ore.

According to the present invention a gas pressure blasting device of the kind having outlet ports controlled by a valve to close them while gas is being introduced into a gas chamber forming a part of the device, wherein said valve is held in closed position by a stop member of a strength which will permit it to withstand a predetermined pressure and which when the gas pressure Witl'lin the chamber is built up by the admission of gas from outside the wall through a gas conducting conduit exceeding the pressure which it will sustain yields and releases the valve which moves in response to the pressure acting therein to a position at which the discharge outlets are opened so that there is a sudden release of 'the gas confined in the chamber is characterised in that the wall of the chamber has a jacket for a portion of its length, in that the jacket is provided with a water inlet nearer to the end of the jacket nearer to the gas inlet into the chamber and with a water outlet nearer to the end of the jacket nearer to the outlet ports and is further provided externally with two annular retaining members between which there extends a collar of rubber-like sheet material forming a gas tight seal at its ends in said retaining members, wherein the rubber-like material is adapted to'assume a bulged contour and thus grip the mine are such that the only kind of explosive permissible to introduce therein is one which contains sufficient quenching agents to prevent a cartridge of the explosive from igniting a gassy atmosphere when it is fired, irrespective of anywatcr in the borehole.

It would be thus desirable to effect the blasting of coal and like materials in gassy mines by means of a sudden discharge of compressed air or other gas froin a suitable apparatus into a borehole already infused with water under pressure. The sealing of an infusion device into a borehole to be infused with water under substantial pressure of the order desired for water infusion can be achieved by means of a cylindrical rubber washer which is squeezed for example by a member acted upon by a.

wall of the borehole in which the device is inserted and form a seal therewith when subjected to gas pressure from within, in that means is provided for the introduction of gas into the space formed between the inner surface of said collar and the outer surface of said chamber at a pressure above the desired maximum pressure of the water in the borehole but below the pressure which the valve stop members can sustain, and in that said retaining means and collar are intermediate in position between the water inlet and outlet from said jacket.

The means for the introduction of gas between the inner surface of the collar and the outer surface of the chamber may be a conduit communicating across the jacket between the chamber and the outer surface of the outer wall thereof beneath said collar, the gas supply to the device being provided with a reducing valve which can be manipulated to give a choice of pressures. The Width of the collar is advantageously somewhat greater than the distance between the stops provided by the retaining members so that it is normally somewhat arched in contour, and the ends of the collar under the retaining members are advantageously reinforced with a metal sheath to maintain them plane during the distortion of the collar under the gas pressure.

In using the device it is introduced into the borehole with the venting outlets and the water outlet from the jacket facing the closed end thereof, so that the water inlet and the gas inlet face towards the mine. The coal would usually be undercut. The gas outlets of the device normally diverge as they pass through the metal from the end of the device facing the closed end of the borehole. The device is introduced sufficiently far into the borehole to ensure that the whole length of the rubber-like collar is within it. The water supply is then turned on. The water passes through the jacket into the gas supply, e. g. compressed air, is then turned on at a' controlled pressure through the reducing valve so that the pressure in the device is below that required tooperate the discharge valve but above the maximum water pres: sure intended to be used in the borehole, for example the air pressure at this stage may be 2,000 lbs/ sq. in. The air escaping into the space between the external surface of the device and the rubber collar bulges the latter outuntil it makes effective contact with the wall of the borehole. and seals the latter firmly. The water pressure beyond the seal causes the water to be forced'th'rough the fissures of the neighbouring strata and sooner or later the water begins to seep through the coal face. The reducing valve is now manipulated s thatthe air. pressure required to cause the stop member to fail is admitted into the apparatus, and whenthe stop. member yields the main air valve opens, the air is suddenly discharged into the waterfilled borehole and the shock of the discharge is transmitted through the water so that a blasting elfect is obtained.

The invention is' illustrated in the accompanying diagrammatic drawings in which Figure 1 shows a section through a face to be blasted with the blasting device in position and Figure 2 shows an axial section of the blasting device. In Figure 1, 1 is the gallery floor,.2 is the roof, 3 is the shothole, 4 is the space from which coal has been removed by undercutting, 5 is the blasting device, 6 is the water supply line to the blasting device 5, 7 is the gas supply line to the blasting device 5, 8 is a pressure reducing valve and 9 and 10 are stop valves. In Figure 2' gas is ledin'to the gas chamber 11 through the inlet 12 and through the conduit '13' into the space 14 behind the collar of rubber-like. sheet material "15 which is held in position by the annular retaining members 16. Water is led into the jacket 17 through the inlet 18 and leaves via the outlets 19. The gas inlet 12 passes through the cap 20 which is threaded on to the closure 21 and through the adaptor 22 which is also threaded on to the closure 21. The venting head 23 is provided with venting ports 24 which are closed by the valve 25. The valve 25 r 4 has attached to it a rod 26 which is retained in position by a metalcotter pin 27 which passes through the hole 28. A removable end fitment 29 is screwed into the venting head 23 to make provision for the removal of any parts of the pin which might remain in the device after blasting.

What we claim is: -l. In' a gas pressure blasting device of the kind inv eluding an elongated housing having outlet ports adjacent one end thereof controlled by a valve adapted to open at a predetermined pressure and in which gas pressure is built up by the admission of gas from outside, the improvement which comprises: an annular jacket surrounding a portion of said housing adjacent the end thereof opposite said outlet ports; said'jacket being provided with longitudinally spaced water inlet'and outlet means whereby water may be introduced into a borehole after the blasting device has been positioned therein; an external annular collar ofrubber-like sheet material surrounding said jacket intermediate said water inlet and outlet means; annular members engaging the ends of said collar and saiddevice for retaining said collar in position; means for. introducing gas into said. collar for inflating said collar to form a fluid seal with the bore hole in which the device is inserted, the pressure of such gas being above the desired maximum pressure of water in the borehole but below the operating pressure of the valve as the basting gas is beingcharged into the blasting device.

2. A gaspressure blasting device is claimed in claim I whereinthe means for the introduction of gas to inflate said collar is a conduit communicating across the jacket beneath said collar.

3. A gas pressure blasting device as claimed in claim 1 whereinthe ends of the collar under the retaining members are reinforced with .a metal sheath to maintain them plane during the distortion of the collar under the gas pressure.

References Cited in the tile of this patent UNITED STATES PATENTS 

